Phase separation dynamics of polycarbonate/polymethyl methacrylate blends. I. Temperature jumps into an immiscibility loop

Abstract

Time-resolved light scattering was employed to elucidate the dynamics of phase separation in mixtures of polycarbonate (PC) and polymethyl methacrylate (PMMA). Blends of PC and PMMA of moderately low molecular weight reveal the coexistence of an upper critical solution temperature (UCST) and a lower critical solution temperature (LCST), forming an immiscibility loop. Temperature jump (T jump) experiments were conducted on the 40/60 PC/PMMA composition from a single phase (150 °C) to a two-phase immiscibility loop region (180 and 190 °C). Phase separation takes place through spinodal decomposition (SD). The early stage of SD is explicable in terms of the linearized Cahn–Hilliard theory. The late stage of SD follows the power law relationship with the exponents of −1/3 and 1 as predicted by the cluster theory of Binder and Stauffer. The universal curve with reduced variables Qm and τ was established. The late stage data were analyzed in accordance with the recent scaling law of Furukawa. The temporal phase decomposition appears to be self-similar. The shape of the structure function can be scaled with slopes of 2 and −6 for q<qm and q>qm regions, respectively.